1. Field of the Invention
The present invention relates to a printing head, and particularly, to a printing head using a resin material as a support member to which a printing element substrate in the printing head is bonded.
2. Description of the Related Art
A printing technology by an ink jet printing method is known as a quiet printing method which is low at running costs. For providing an ink jet printing apparatus at a lower price, it is effective to advance low pricing of a printing head which ejects ink droplets and occupies a high percentage among total costs of the ink jet printing apparatus. A printing element substrate which is a chip for ejecting ink is highly accurately positioned, attached and fixed on a surface with which a printing head is provided. In many cases of the printing head which has advanced the low pricing, the attachment surface on which the printing element substrate is attached and fixed is constructed of resin material. This is because it is possible to produce the printing head at a lower cost by using an injection molding technology as compared to a case where the attachment surface of the printing element substrate is constructed of a material other than the resin material, for example, a ceramic material.
Incidentally, for securing a printing quality at a high grade upon mounting the printing head to the ink jet printing apparatus, it is required to accurately maintain and control dimensions from a mount reference surface of the printing head to an orifice through which ink of the printing element substrate is ejected. Therefore, a high planarity is required on an attachment surface of the resin member to the printing element substrate. It is preferable to make uniform a molding contraction rate of a molding resin for the realization. Therefore, it is required to make uniform a thickness of a sheet-shaped portion of the support member to which the printing element substrate is attached, as much as possible. Further, for promoting cost cutting, in many cases, configurations of an ink passage for supplying the ink to the printing element substrate and a mount portion of a filter removing dusts in the ink are formed by support members made of the same resin member. In this case, a thickness of the sheet-shaped portion of the support member to which the printing element substrate is attached may be possibly increased. In general, a recess called a sink mark may be generated on a surface of a thick-walled portion in a resin component formed by injection molding. For preventing occurrence of such a recess on the attachment surface of the printing element substrate, a cavity portion is formed in a back side of the attachment surface of the printing element substrate and the wall thickness of the attachment surface is reduced. Therefore, it is possible to make uniform the thickness of the sheet-shaped portion of the support member to which the printing element substrate is attached. The printing head of such a construction is disclosed in U.S. Pat. No. 7,063,411. Since the cavity portion is formed in the above printing head, a physical strength of the wall constituting the cavity portion is degraded.
In consequence, in a case where, when the printing head in which the cavity portion is formed is mounted to the printing apparatus, the printing head falls from a high place by mistake and an impact shock is given on the above portion of the printing head in which the physical strength is weak, the printing element substrate provided in the printing head is deformed, possibly causing a printing defect.
Especially when the printing head which has fallen collides with a floor or the like, the attachment surface of the support member with the printing element substrate is deformed by the impact shock of the collision, thereby possibly damaging the printing element substrate. In this case, since the printing element substrate is attached and bonded to the support member by an adhesive or a sealant for sealing the periphery of the printing element substrate, the deformation of the attachment surface of the support member is supposed to deform also the printing element substrate through the adhesive or the sealant of the periphery in the printing element substrate. In this way, the deforming of the printing element substrate is undesirable for adversely affecting the printing quality.
Particularly, in a case where a rectangular ink supply opening penetrating through the printing element substrate is provided in the printing element substrate, when the printing element substrate is deformed by the impact shock given to the printing head, the deformation possibly affects further the printing grade. This ink supply opening is formed by an anisotropic etching process method and has corner portions. In consequence, the aforementioned deformation of the printing element substrate concentrates on the corner portion of the ink supply opening. When the stress to the corner portion due to the deformation is excessively large, a crack possibly occurs in the printing element substrate. The crack of the printing element substrate may cut wires or the like inside the printing element substrate to cause the printing defect.